Descended from the MIDI sequencer and the digital audio sequencer, multitrack loop sequencers represent a third generation in the evolution of sequencing software. By making it possible to easily tempo-match and layer audio loops, loop sequencers have already changed the way thousands of artists make music. Although the programs covered in this roundup are often surprisingly powerful and versatile, they all center on the lowly loop.

LOOPOLOGY

For the purposes of this article, I'll define a loop as an audio file or a section of an audio file that is designed to play repeatedly. Loops are often short recordings of rhythm parts and are used as “building blocks” within larger arrangements. When a loop is edited correctly, it produces a smooth, continuous pattern. If the editing is sloppy, you'll hear a pause, an increase in speed, a hiccup, or some other anomaly.

When people first started working with samplers and digital audio sequencers, they naturally tried to layer different audio loops. That often proved to be problematic. If two loops aren't the exact same tempo and the exact same length (or an even multiple or fraction thereof), they just won't lock. The loops must match, and match well, or they will quickly drift apart.

SLICE AND DICE

The programs in this roundup solve the loop-matching problem by viewing each audio file as a series of individual notes, drum hits, or segments typically referred to as slices. First popularized by Propellerhead ReCycle and Sonic Foundry Acid, loop slicing lets you change the tempo and duration of a loop while retaining the original sound and pitch of the music.

Slicing doesn't really alter the sounds of the instruments. It just chops each loop into a series of notes and plays the notes at the designated time. When you slice up an audio file, you create an edit list or playlist that is tied to the composition's tempo.

That's a better approach than using digital-signal-processing (DSP) time-stretching algorithms to expand or contract loops. Aside from their other limitations, time-stretching algorithms almost always color the sound and frequently yield unnatural results. In addition, they demand considerable processing power.

When you import an audio file into a loop sequencer, the program uses a process called transient detection to determine where the beats are. The program slices the file into segments, placing a marker before the major transients (peaks).

Some programs also superimpose a tempo grid, placing a slice marker at note intervals (such as every quarter note, eighth note, or 16th note). Markers can usually be adjusted manually, but you rarely need to touch them — the automatic marker placement is generally dead-on in all of the programs surveyed here.

Keep in mind that in most cases, the audio file is not actually being segmented. Rather, the program creates and modifies a list of the markers, pointing to time positions within the original audio file. It's that list of marker times that gets manipulated when you change the tempo. Slicing not only makes it simple to change the tempo of loops but it can also let you quantize loops, derive groove templates from audio files, and perform wholesale drum and instrument replacements. (These programs also offer separate pitch-shifting functions so you can properly match pitches as well as tempos.)

Think of the loop as a kind of musical building block consisting of the original WAV or AIFF audio file along with the slice marker list and usually other information, such as the detected tempo or assigned key. Manufacturers use proprietary technology to implement this shiftable loop package; the REX2 and Acidized formats are supported by some of the originators' competitors. As you'll see, the need for preformatted samples is starting to disappear. (See the table “Looper Specs” for a list of supported file formats and other details.)

Most of the programs in this roundup are available for PCs with Pentium processors running most of the recent versions of Windows, including 98, ME, 2000, and XP. Three of the programs run on Power Macs with Mac OS 8.6 or higher.

This article omits a number of me-too or junior-edition programs, and it centers on the middle and upper ranges of the price and functionality spectrum. (See the table “In Review” for a list of the programs that have received full reviews in EM.) All the programs in this roundup are multitrack layering environments with the exception of ReCycle, the one that started it all. (You'll also find an alternative approach to loop manipulation in the sidebar “Ain't That a Groove.”)

RECYCLE (MAC/WIN)

Propellerhead Software (maker of ReBirth) started the loop-slicing madness back in 1994 with the original ReCycle. The EM editors liked version 1.0 so much they gave it an Editors' Choice award the following year. ReCycle 2.0, released in 2001, keeps this venerable tool relevant in the 21st century.

Designed as an adjunct utility for audio-editing and multitrack software, ReCycle pretty much does one thing: it offers better time shifting through loop slicing — and it slices loops exceedingly well (see Fig. 1). Propellerhead has addressed a number of the original version's shortcomings — for example, ReCycle now handles stereo files — and the company has kept the program focused, fast, and simple.

ReCycle lets you adjust the tempo of any loop and export it as a new WAV or AIFF file. Make sure you remember to select Transmit as One Sample from the Process menu when you want a single file. Otherwise ReCycle's default settings will cause it to save each segment in the loop as a separate audio file. If you have a sampler, you can then load the slices into a new preset and trigger the slices using any sequencing software. ReCycle even exports a Standard MIDI File beat map for that purpose.

Click on image to enlarge FIG. 1: Propellerhead ReCycle pioneered the loop-slicing concept; the vertical slice-marker lines in the waveform dislay can be created automatically or by hand.

Once a groove has been broken down to the component drum hits and their sequence of Note On times, you can easily adjust the tempo, quantize the performance, or replace any of the sounds.

ReCycle's proprietary REX2 files can be imported as a single audio track into a REX2-compatible sequencer (such as Reason, Emagic Logic Audio, or Steinberg Nuendo or Cubase VST) and played back with control over the tempo. According to Propellerhead, REX2 support in Mark of the Unicorn (MOTU) Digital Performer is forthcoming.

ReCycle supports direct SCSI transfer for major hardware samplers, and it offers MIDI sample-transfer capability and special Akai-format support. (ReCycle is the only program in this group that provides specific sampler support.) The software includes a handful of basic DSP processes, such as normalization, DC-offset correction, real-time EQ, compression, and pitch shift.

ReCycle ran without a hitch during my tests. If you've ever used sound-editing software, it'll take you ten minutes or less to figure out how to work with the program.

ACID PRO (WIN)

Sonic Foundry Acid's innovation was to deploy ReCycle's loop-slicing paradigm on a multitrack level. The program has been through a couple of overhauls since its 1998 release, and Acid Pro 3.0 (see Fig. 2) retains its position at the head of the pack.

Click on image to enlargeFIG. 2: Sonic Foundry Acid was the first loop-slicing multitrack. It's easy to preview files in the browser view and then drag the files up into the track display for arranging and processing.

Acid Pro lets you drag time-shifted loops, MIDI files, long digital-audio files, and even a video file into an arranging window with one file per track. In that respect, it's different from other audio multitrack programs, which typically let you put multiple files into a single track. With Acid Pro, you end up having more tracks, which could be a detriment when adding real-time effects.

New in Acid Pro 3.0 is the Beatmapper, which handles song-length files, dropping markers and controlling tempos across long recordings. MIDI playback and recording is another big new feature. It's quick and simple to configure the program, start recording, and edit in the Piano-Roll view.

Also new in 3.0 is DLS (Downloadable Sound) playback support and video scoring. AVI and MOV (QuickTime) files open as a “filmstrip” in the Track view. The strip display resizes nicely; zoom in far enough, and you can spot audio cues with frame accuracy. There's also an optional video display in a small dedicated window, and Acid Pro supports external video displays, which is really the way to go when syncing sound to picture.

Unfortunately, you'll be a bit disappointed if you try to import an MPEG video into Acid Pro. A dialog box appears and states that a plug-in purchase is required. And forget about trying to edit the video strip in any way from within the program. When you click on the video track, built-in ads for Vegas Video and Video Factory pop up.

Any skimping in the video department, however, is in marked contrast to the audio side of the package. The Sound Forge XP Studio 5.0 audio-editing software and the Vegas Audio LE multitrack program are bundled with Acid Pro. The package also includes CD-ripping and -burning capabilities and 18 DirectX audio plug-ins.

When it comes to looping audio, Acid Pro is king. You can just open and play any session, go into the Explorer display, click on Auto Preview, and then single-click on any audio loop in your collection. Better yet, use the arrow keys to scroll quickly through whole folders of loops.

You'll notice that loops are previewed in sync with the session. If they're cut correctly, loops that haven't been previously Acidized are previewed at the session tempo. That's an important point: Acid Pro 3.0 slices and tempo-shifts loops before you even import them into the program! That's what I call performance. Acid Pro anticipates your needs and graciously provides the solution.

Acid Pro has multipurpose faders in the Track display as well as a Mixer window that displays all channels, buses, and effects. Volume, pan, and effects sends can be automated and edited using conventional break-point envelopes.

I discovered an undocumented feature in Acid Pro: Paint Brush erase. With the Paint tool selected, you can right-click on the Track display to delete events. It's faster than switching to the Eraser and works only with the Paint tool, not the Pencil tool. It's a little quirky, but it's convenient.

Acid Pro 3.0 has only a few shortcomings. As mentioned previously, it's strictly a one-file-per-track program. There is no support for alternate meters such as 5/4 or 7/8, and it notably lacks effects-parameter automation, although it does let you automate effects-send levels. Acid Pro doesn't have DXi or VST Instrument support. Also, Acid Pro's graphic-editing tools are “modal”; you'll find yourself constantly having to switch between the Pencil, Paint, Selection, and Eraser tools. As trade-offs go, however, those are a small price to pay for the outstanding looping performance, easy audio and MIDI recording, overall ruggedness, and sensible layout of Acid Pro.

PLASMA AND SONAR (WIN)

At a suggested retail price of $49.95, Plasma is Cakewalk's attempt to grab the low end of the looping market, and it competes vigorously with Sonic Foundry's Acid Music junior edition. Plasma delivers the important bread-and-butter features, and it also provides sufficient power to get some real work done.

Click on image to enlarge FIG. 3: You can drag files from Cakewalk Sonar's browser window (foreground) into the track-arranging display (background); Plasma looks almost exactly the same.

Plasma looks and works a lot like Cakewalk's high-end Sonar sequencer (see Fig. 3). From the user-configurable toolbar right down to the identical windows and dialog boxes, Plasma is “Sonar Junior” with an emphasis on looping features.

Plasma and Sonar both feature a Loop Construction window that is highly reminiscent of ReCycle (see Fig. 4). Instead of offering one slider, Plasma has two: you can generate markers based on transient detection or simply apply a grid of note-length intervals. Creating new markers by hand requires a fast double-click, which is trickier than it sounds.

Whereas the default behavior of Acid is to slice files without asking, you have to tell Plasma and Sonar to slice each time by clicking on the Enable Looping button in the upper-left corner of the Loop Construction window. Cakewalk representatives say that's necessary because Sonar doesn't deal exclusively with loops. You can also import other audio data into projects. Be that as it may, it's just not as slick from a loop-centric perspective.

Once a file is sliced and looped, it's easy to “paint” blocks across the track window and start building an arrangement; there are no confusing drawing tools in Plasma.

The Loop Explorer view appears in Plasma and Sonar as a simple floating window. It lets you sort, view, and audition any supported audio file. The Loop Explorer's Auto Preview function plays audio files that are not yet part of your session as you click on them in the display. You can even preview as many as 16 loops simultaneously!

Click on image to enlarge FIG. 4: In the Sonar and Plasma Loop construction view, Beat Grid size and Transient Detection sensitivity are controlled by the two sliders above the waveform display.

If the selected audio file is a preprocessed “Groove” or Acidized clip, the file will time-shift and preview in the current project tempo and key. If the file is simply a new WAV or AIFF file, it previews at its original tempo, out of sync with the session. Unfortunately, that's not quite at the level of the previewing found in Acid Pro (or Ableton Live, which I'll cover later).

Cakewalk's extensive experience in developing MIDI sequencers really shows in Plasma and Sonar. MIDI and audio production require a deep and complex tool set, and neither Plasma nor Sonar skimps on the features. Nevertheless, it's as easy to sequence in Plasma or Sonar as in any program that I've ever used. Both programs offer unlimited audio and MIDI tracks, video import/export, support for automatable DirectX 8 effects plug-ins, support for alternate meters (Brubeck, here we come), unlimited layers of Undo, and fairly straightforward multitrack audio editing and automation. Moreover, both packages come with lots of DSP effects plug-ins and loop libraries.

Any gripes I have about Sonar or Plasma are essentially philosophical. For example, Plasma and Sonar rely on the current-time cursor position as the starting point for paste operations instead of using the edge of the current clip or track selection. That forces you to reposition the cursor before every paste. It can slow things down and seems counterintuitive.

Nonetheless, Plasma and Sonar provide everything that you would typically expect in a loop sequencer and a whole lot more. They're feature-rich and largely well-designed products capable of producing high-quality professional works. Though certain parts of Plasma and Sonar (such as basic MIDI recording) are dead simple, other aspects may have you scratching your head at first. By the time you figure out basics such as the toolbars and Channel Strip, however, you'll be cruising along.

Some aspects of the looping implementation in Plasma and Sonar may not be as slick as Acid Pro and Ableton Live. But by including things such as automatable plug-in effects, multiple files per track, alternate meters, and DXi synth support, Plasma and Sonar offer much more complete sequencing tool sets.

FRUITYLOOPS 3 (WIN)

Developed by the Belgian company Image-Line Software, Fruityloops 3 is a self-contained production environment for electronic dance music. Centered on a step-sequencing window (see Fig. 5), Fruityloops is not really an audio multitracker or a MIDI sequencer; it's more of a post-ReBirth groove machine on steroids. “Techno playhouse” might be an apt description.

Image-Line packs a lot into the step-sequencing metaphor, and not just drums and bass-line generators. You'll also find soft synths galore, sample playback, and time shifting. Composing in Fruityloops entails assigning sounds to the step sequencer and setting up patterns that are then arranged in the Playlist window. One of the possible sound sources is a sliced-up loop.

I worked with the full version of Fruityloops, but a scaled-down Pro version is available, too. That package lacks automation, ASIO support, and a piano-roll display. Fruityloops represents the modular approach to software design; things such as editors and additional soft synths are available as separate purchases. The same is true of time stretching, which is not built in to Fruityloops as an integral central feature the way it is in Acid and Live.

Grooves exported from BeatSlicer are laid out in steps as in ReCycle, one segment per step-sequencer channel. The terraced output makes it incredibly easy to go nuts with drum-replacement surgery, allowing you to switch out every hit and still retain much of the original feel.

BeatSlicer works with another included Fruityloops plug-in called Fruity Slicer. It lets you split up any WAV file and lines up the slices in the step sequencer. A Fruity Slicer playlist takes up a single channel on the step sequencer and is much easier to manage than the sprawling BeatSlicer exports.

Fruityloops doesn't do audio recording and multitracking in the conventional sense, and that's no mark against it; it's a different type of program. It has a straightforward and rather cool piano-roll editing interface and allows you to play MIDI sequences right into the beatbox. The MIDI setup was difficult to use, and I had to enlist the help of an Image-Line representative to get my keyboard and sound modules talking to the program.

The program has some really intriguing aspects, such as the Fruity Scratcher effect plug-in. (Sadly, that module is completely undocumented.) Certain controls, such as the channel mutes, are hard to identify. (Check for the tiny green lights along the left side of the step window.) In addition, most functions in Fruityloops are buried three layers down within submenus. It's not exactly a dive-in-and-use-now program.

Fruityloops makes several disorienting departures from typical Windows interface conventions, including unusual uses for the right mouse button. I also found some glaring errors in the manual; certain things have been relabeled since the last printing. That kind of unprofessional lapse might lead you to conclude that this is more of a grand toy than a workhorse production system.

Nonetheless, there is plenty to like about Fruityloops 3. For example, nearly all effects parameters are easily automatable by mouse or external MIDI controller. The program is full of nifty novelties such as a two-knob plucked-string synthesizer and the Beepmap graphic-to-audio plug-in. The designers have thoughtfully put resonant filters nearly everywhere you turn, and the program places little strain on the CPU. It ran smoothly at all times.

I would prefer it if Fruityloops' loop-slicing features were more tightly integrated and the program didn't require the purchase of a second product from another company, although the interoperability between Fruityloops and BeatSlicer is quite reliable. According to the company, many people prefer Image-Line's modular approach to software.

PHRAZER (MAC)

BitHeadz is best known for its beloved Retro AS-1 software synthesizer and Unity DS-1 software sampler. Released in 2000, Phrazer was for a time the only looping multitracker on the Macintosh (see Fig. 7). At this point, Phrazer could use an upgrade, although it delivers a basic Acid-type experience on the Mac platform and still does some pretty cool things.

Click on image to enlargeFIG. 7: BitHeadz Phrazer was the first multitrack loop sequencer for the Mac. The sliders at the bottom of the screen are for a compressor effect.

At first glance, Phrazer is similar in layout to Acid, Sonar, and Live. It has a file-browsing window and a track display with an edit window. You drag files in, slice them, and arrange them, all under master tempo and key control. Phrazer lets you place any number of loops in a single track, which is preferable to the Acid one-loop-per-track approach.

Phrazer has no MIDI sequencing and fairly rudimentary audio editing but makes up for those shortcomings with interoperability: it includes MOTU Audio System (MAS) output and FreeMIDI input for MOTU Digital Performer compatibility. ReWire support allows Phrazer to route audio to a Steinberg Cubase or an Emagic Logic Audio track, and DirectConnect provides a comparable service for Pro Tools users.

Another nice touch in Phrazer is that MIDI notes and QWERTY keystrokes can gate tracks or trigger one-shot audio files. This good idea is also implemented in Ableton Live. One feature that is not seen in Live is MOV support. Phrazer lets you import any QuickTime movie, spot audio to the frames, and export the video with the new soundtrack. Phrazer also reads Acid 2.0 files.

Phrazer employs what BitHeadz calls Munge dialog boxes and the Munge menu, which could be a source of confusion because the term is never really defined. Munge is a rather obscure and slightly derogatory term that usually means to imperfectly transform information. Munge can also mean to change data in some way that can't or won't be explained. In this case, it's Phrazer-speak for a “process” or destructive edit.

In Phrazer, most of the audio processes, including Crop and Normalize, as well as the loop tools are concealed beneath the Wrench button (see Fig. 8). It's too bad those basic features were not made more accessible through keyboard shortcuts or a redundant Process menu.

Click on image to enlargeFIG 8: The Munge menu is revealed by clicking on the wrench button beneath Phrazer's Track view.

Other important tools are likewise hidden away. To insert a track effect or add an automation event, you must hold down the Control key while clicking on a Track display block — not the most obvious move. You can also get to the effects selection from the Edit menu by choosing Add Event. Inserting real-time effects is an important feature in any audio program; it merits some salient onscreen control or at least a menu option with the word effect in it.

Phrazer's built-in effects sound acceptable, but their controls are rudimentary, and I was quite surprised to find no effects presets or factory patches. You also won't find effects-parameter automation or VST plug-in support, things that most users have come to expect.

Speaking of omissions, there is no mixer automation editing using break-point envelopes. Phrazer does let you insert volume and pan “events” into the Track display, a somewhat unusual and rather counterintuitive way of mixing. In addition, you can't scroll the Track display by dragging a selection offscreen, and there is no way to relocate playback by clicking in the Track display; you must use the Transport palette.

When importing a new sample, Phrazer interrupts the process with three dialog boxes. The first asks if you want to enter split points. The next dialog asks if you want to “correct” the tempo of your loop. (The tempo must match the length and number of beats of the sample, and by its default settings Phrazer usually thinks it detects a mismatch.) Finally, the Sample Munge Tempo dialog appears, in which the user helps the program calculate the loop tempo.

One could argue that Phrazer is essentially a dedicated looping application. As such, it might have served users better by assuming that most imported audio files are in fact loops. It could then go ahead and slice them and calculate the darn tempo without human intervention. Ask About Tempo and Ask Default Split Points can be turned off. Unfortunately, deselecting those options doesn't get you automatic slicing and tempo calculation; it just suppresses the dialogs and makes you initiate slicing or calculation in every case.

Phrazer has two modes of slicing: transient detection and beat grid. The program provides slider control over slicing, and though the results are acceptably accurate, the implementation is nowhere near as keen as in ReCycle or Plasma.

Phrazer's PDF-only owner's manual is a fairly good attempt. It includes several errors, however, and it's peppered with the kind of annoying typos that a spelling and grammar check could catch. I'd like to see a hard-copy manual with a few tutorials, some online help, an upgraded program, and a more streamlined looping procedure. If Phrazer were a low-cost program — less than $100 — I would be less critical of it. But at $299, most Mac users will likely turn to Ableton Live instead.

LIVE (MAC/WIN)

Straight out of Berlin, Ableton Live is the only multitrack loop sequencer that runs on Mac and Windows. It's also a great-looking program, establishing a new style for audio software.

Smartly sidestepping the sequencer-feature wars, Ableton positions Live as a loop-sequencing instrument meant for real-time jamming. With the advent of underground laptop-computer music and a growing number of mainstream acts of every stripe taking computers onstage, live performance could well be a growth niche for the music-software biz.

Like Phrazer, Live lets you place multiple loops in each track and tracks in Live respond to MIDI Note On messages or QWERTY keystrokes. The similarities end there, however, because Ableton takes loop sequencing in a whole new direction.

Click on image to enlargeFIG. 9: Ableton Live's mixer is where most of the arranging work takes place. Filter Delay and Compressor effects are seen in the lower section; all parts are automatable.

Although Live has a track-arranging display, the program is centered on a mixer (or Session) window (see Fig. 9). What's unique is that you drag audio files into the mixer, stacking up as many loops, one-shots, or long files as you like in each mixer strip. You can play each clip by clicking onscreen Play buttons, or you can assign them to any MIDI note or computer key. Naturally, all looped audio is time shifted, so it stays in tempo with the session.

By de-emphasizing the Track view and block-arranging while featuring the straightforward, improvisatory Session interface, Live provides one of the fastest composition environments available. It combines file-browsing and effects-selection functions in one multipurpose panel along the left side of the screen.

The program has ten built-in effects, five of them variants on the delay line. Each effect is cleverly implemented, includes intuitive graphic controls, and has parameters that are fully automatable by MIDI controller or onscreen dragging. VST effects plug-ins are supported on Mac and Windows, but sadly, there is no DirectX plug-in support on the PC. There's also no MIDI sequencing and no real audio editing, although Live does allow you to record on the fly and to define a loop from within a larger file.

Although files can be dragged from the browser into the linear arranging display, the hip way to arrange is in real time. Turn on the record function and start firing clips you've loaded into the mixer; selections are recorded, and they can subsequently be viewed and edited in the Track window. All volume, pan, or effect-parameter changes are also recorded and played back; the conventional break-point automation envelopes can be edited in the track display.

Live includes several nice touches, such as zoom navigation. Rather than using a conventional magnifying glass, you click on a tiny file overview and drag to select a zoom range and center point (see Fig. 10). It's a unique and fluid way of zooming. (For a differing opinion about this feature, see Erik Hawkins's review of Ableton Live on p. 116.) Another elegant refinement is Live's three file-browser views. Each can be set to a different root directory, sparing you from having to view the entire file structure.

Click on image to enlarge FIG. 10: Click on the Zoom toolthe blue bar just below the waveform displayto scroll and zoom within Live's Clip view.

Live includes detailed contextual help: hold the mouse pointer over any onscreen widget, and a complete description appears in the lower-left quadrant. To get rid of the Help display, click on the arrow in the lower-left corner.

High performance is the ultimate refinement. Like Acid Pro, Live lets you preview loops at session tempo, even loops that have not been presliced. You can let your session roll and then arrow-key through Live's file browser to audition batches of loops in time with your composition. As long as the loops have been cut correctly, they'll sync.

Windows users will notice that no functions are assigned to the right mouse button; Live's PC version mirrors its Mac twin in nearly all respects. I wish Live supported more file formats — such as SDII, MP3, or Red Book (CD) audio — but with conversion tools readily available elsewhere, the lack of built-in file support is by no means an insurmountable problem.

Other programs allow more control over the slicing process, letting users independently move or manually create slice markers. Live is a little more restrictive in that regard and a little more automated in its slicing; in practice you are not likely to need or miss the extra work.

Live has support for song-length files, much like Acid Pro's Beatmapper, and it includes a Warp Points feature that lets you tie the session tempo grid to markers within a sample. Any tempo variations within the file can be followed by the rest of the session, or a file with varying tempo can be made to conform to an unwavering tempo grid. Live will also sync to MIDI Time Code or MIDI Clock, and it plays nicely with other applications running on the same computer.

In terms of sheer features, Live is the clear winner over its Mac-platform competition. Its looping performance and ease of use are as evolved as any Windows entry — equal to Acid Pro, yet very different and wonderful in their own right. Easy to use, reliable in operation, and sexy to look at, the program competes well against all other loop sequencers. By adding a well-planned real-time layer, Live has carved out a unique and distinctive niche among loop sequencers. It's certainly worth a test drive by both Mac and Windows adherents.